This invention relates to a special motion reproduction system for producing special-motion effects, such as slow motion, quick motion, still motion and other effects, in television video signals reproduced by a helical-scan video tape recorder player (VTR) while a magnetic tape is transported at a tape speed different from the recording tape speed, and more particularly to a video head deflection apparatus therefor.
Several systems have been proposed to record and/or reproduce television video signals on a magnetic tape. One of them is a helical-scan VTR wherein a tape wrapped around a drum including a rotary head is transported to form video tracks on the tape which are diagonal with respect to the longitudinal direction of the tape. The helical-scan VTR is widely used by consumers, industry and by professionals in broadcasting stations. In the helical-scan VTR, the video signal of one or more fields is recorded on a video track, and the rotary head is rotated in synchronization with a vertical synchronizing signal for the input video signal to be recorded.
In case where the video signal of one field is recorded on one video track, the rotation of the rotary head is so controlled that the vertical blanking portion of a television signal is recorded at the end portions of each video track (the margin of the tape). Such control is accomplished by phase comparison between a tachometer signal representing the rotating phase of the rotary head and the vertical synchronizing signal of the input video signal. Accordingly, the vertical synchronizing signal for the input video signal maintains a predetermined phase relationship with the tachometer signal in the record mode.
For reproducing the recorded video signal at normal speed, the rotary head is controlled so as to rotate at predetermined rotational speed (revolutions per minute) in synchronization with the synchronizing signal being supplied from the sync signal generator or other reference signals. One conventional way to achieve this result is that the running phase of the tape is controlled by, for instance, the rotation of the tape driving capstan so that the rotary head follows the center of a video track (achieves "tracking").
In special-motion effects reproduction wherein only the tape transport speed is varied from the normal tape speed (at which the video signal was recorded) to produce a special motion effect, the rotary head scans the tape in a path different from the recorded video track. In tape stop mode, the rotary head which started scanning in the vicinity of one end (for example, lower end) of the tape and which was in perfect alignment with a video track would find itself scanning the adjacent video track when it reached the vicinity of the other end (for example, the upper end) of the tape. Therefore, the rotary head scanning a specific video track will gradually depart from the track until it begins to scan the adjacent track.
The signal pattern on a tape recorded with a helical scan VTR is usually such that a guard band is provided between video tracks, with the width ratio of video track to guard band being about 2:1. Therefore, as the rotary head gradually loses alignment with a track, the S/N ratio of video signal decreases and as long as the head is scanning two tracks at the same time, a beat interference occurs, resulting in considerably deteriorated video quality. When the tape in the stop mode is caused to run slowly in forward direction (normal transport direction) or reverse direction, a slow motion effect is produced in the video scene according to the tape transport speed, but in this case, too, the rotary head loses tracking, and a video band containing noise or beat interference will appear in the picture and will move upward or downward depending on the tape transport speed.
To eliminate such undesired deterioration of the picture being reproduced in the special motion modes, automatic scanning systems have been proposed. In such automatic scanning systems, as described, for example, in the U.S. Pat. Nos. 4,080,636, 4,093,885, 49,099,211, and 4,106,065, the rotary head is mounted on a deflectable end portion of a piezoelectric bimorph and is deflected perpendicular to the video track, i.e., to the rotating direction of the rotary head so that it will not lose alignment with the track. However, such automatic scanning systems have complicated video head deflection apparatus for deflecting the rotary head.